In modern days, personal digital assistants (PDA) are more and more popular for their portability and convenience.
For portability and size concerns, a typical PDA only has simplified buttons for inputting data, or alternatively inputting data has to be carried out by directly touching a display or a touch pad thereof. Therefore, when a user wants to input complex information, another external input device is needed.
For different hardware specifications of different PDAs, users need different types of external input devices. If users don't want to waste their time preparing different input devices or manually modifying (in some cases, you can't even modify it at all) the same input device to various PDAs, they really need a new solution.